Immersive and experiential computing systems are entering the consumer and industrial markets and have the potential to profoundly impact society. Applications of these systems range from entertainment, education, collaborative work, simulation and training to telesurgery, phobia treatment, and basic vision research.
Virtual reality and augmented reality systems can produce highly-immersive experiences, but they can also cause visual discomfort, eyestrain, and nausea. In every immersive experience, the primary interface between the user and the digital world is a near-eye display. Many characteristics of the near-eye displays can define the quality of a users experience, such as resolution, refresh rate, contrast, and field of view. Despite significant improvements in virtual reality and augmented reality systems, significant sources of visual discomfort can still be experienced during use of such devices.
One of the primary sources of discomfort is often the vergence-accommodation conflict (VAC). In the natural environment, the human visual system relies on a variety of cues to determine the 3D layout of scenes. The extent to which a near-eye display can recreate these cues can determine the quality and comfort of the user experience. Vergence and accommodation are two different oculomotor cues that the human visual system can use for estimating absolute and relative distance of objects. Vergence refers to the relative rotation angle of the two eyeballs; when objects are fixated on nearby, the eyeballs rotate inwards, whereas the opposite happens when objects are fixated on at some distance. The brain can interpret the relaxation or contraction of the extraocular muscles that physically rotate the eyeball as a cue for the absolute distance of the fixated object. The associated visual cue is known as binocular disparity the relative displacement between the images of a 3D scene point projected on two retinal images. Together, vergence and disparity make up stereopsis, which is generally considered a strong depth cue, especially for objects at intermediate distances (i.e. 1-10 m). Accommodation is an absolute monocular depth cue that refers to the state of the ciliary muscles, which focus the crystalline lens in each eye. As with vergence, the state of these muscles varies as a function of the distance to the point at which the eyes are focused. Accommodation combined with the associated visual cue, retinal blur or perceived depth of field (DOF), make up the focus cues, which are particularly useful for depth perception of objects nearby. In normal viewing conditions, the visual cues provide input signals that can be used to adjust the oculomotor responses i.e. disparity drives vergence and blur drives accommodation.
The brain is wired to interpret all of these visual and oculomotor stimuli in a consistent manner, because that is what a person with normal vision experiences in the physical world. In many current virtual reality (VR) and/or augmented reality (AR) near-eye displays, a stereoscopic image pair drives the vergence state of the human visual system to arbitrary distances, but the accommodation, or focus state of the eyes is optically driven towards a fixed distance (i.e. that of the virtual image of the microdisplay). Specifically, many conventional near-eye displays use magnifying optics to create a virtual image of a physical micro-display that is perceived at a fixed optical distance that cannot be changed in software. Hence, retinal blur drives the user's accommodation to the virtual image. The discrepancy between these depth cues hinder visual performance and create visual discomfort and fatigue, and compromised visual clarity. Observed symptoms can be similar to motion sickness.